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also known as Klinefelter's Syndrome

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Men with Klinefelter syndrome, as this group of symptoms has come to be called, have an extra sex chromosome, XXY instead of the usual male arrangement, XY.


In 1942, Dr. Harry Klinefelter and his coworkers at the Massachusetts General Hospital in Boston published a report about nine men who had enlarged breasts, sparse facial and body hair, small testes, and an inability to produce sperm.

By the late 1950s, researchers discovered that men with Klinefelter syndrome, as this group of symptoms came to be called, had an extra sex chromosome, XXY instead of the usual male arrangement, XY. 

In the early 1970s, researchers around the world sought to identify males having the extra chromosome by screening large numbers of newborn babies. One of the largest of these studies, sponsored by the National Institute of Child Health and Human Development (NICHD), checked the chromosomes of more than 40,000 infants.

Based on these studies, the XXY chromosome arrangement appears to be one of the most common genetic abnormalities known, occurring as frequently as 1 in 500 to 1 in 1,000 male births. Although the syndrome's cause, an extra sex chromosome, is widespread, the syndrome itself-the set of symptoms and characteristics that may result from having the extra chromosome-is uncommon. Many men live out their lives without ever even suspecting that they have an additional chromosome.

" I never refer to newborn babies as having Klinefelter's, because they don't have a syndrome," said Arthur Robinson, M.D., a pediatrician at the University of Colorado Medical School in Denver and the director of the NICHD-sponsored study of XXY males. "Presumably, some of them will grow up to develop the syndrome Dr. Klinefelter described, but a lot of them won't."

For this reason, the term "Klinefelter syndrome" has fallen out of favor with medical researchers. Most prefer to describe men and boys having the extra chromosome as "XXY males."

In addition to occasional breast enlargement, lack of facial and body hair, and a rounded body type, XXY males are more likely than other males to be overweight, and tend to be taller than their fathers and brothers.

For the most part, these symptoms are treatable. Surgery, when necessary, can reduce breast size. Regular injections of the male hormone testosterone, beginning at puberty, can promote strength and facial hair growth-as well as bring about a more muscular body type.

A far more serious symptom, however, is one that is not always readily apparent. Although they are not mentally retarded, most XXY males have some degree of language impairment. As children, they often learn to speak much later than do other children and may have difficulty learning to read and write. And while they eventually do learn to speak and converse normally, the majority tend to have some degree of difficulty with language throughout their lives. If untreated, this language impairment can lead to school failure and its attendant loss of self esteem.

Fortunately, however, this language disability usually can be compensated for. Chances for success are greatest if begun in early childhood. Sections that follow describe possible strategies for meeting the special educational needs of many XXY males.

From the National Institutes of Health